diff --git a/workspace/a2a_tools_delegation.py b/workspace/a2a_tools_delegation.py
index 79f42fd1..4fcc2ee8 100644
--- a/workspace/a2a_tools_delegation.py
+++ b/workspace/a2a_tools_delegation.py
@@ -204,6 +204,20 @@ async def tool_delegate_task(
     if not workspace_id or not task:
         return "Error: workspace_id and task are required"
 
+    # Self-delegation guard: delegating to your own workspace ID deadlocks —
+    # the sending turn holds _run_lock while the receive handler waits for the
+    # same lock, the request 30s-times-out, and the whole cycle is wasted.
+    # Reject immediately with an actionable message. (effective_src mirrors the
+    # `src or WORKSPACE_ID` resolution used below for routing.)
+    effective_src = source_workspace_id or _peer_to_source.get(workspace_id) or WORKSPACE_ID
+    if workspace_id and workspace_id == effective_src:
+        return (
+            "Error: cannot delegate_task to your own workspace — self-delegation "
+            "deadlocks _run_lock (your sending turn holds it, the receive handler "
+            "waits for it, the request times out). There is no peer who is also you: "
+            "just do the work yourself, or call commit_memory / send_message_to_user directly."
+        )
+
     # Auto-route: if source not specified, look up which registered
     # workspace last saw this peer (populated by tool_list_peers). Falls
     # back to the legacy WORKSPACE_ID for single-workspace operators.
@@ -323,6 +337,16 @@ async def tool_delegate_task_async(
 
     src = source_workspace_id or _peer_to_source.get(workspace_id) or WORKSPACE_ID
 
+    # Self-delegation guard: even on the async path, queuing a task to your own
+    # workspace just makes you re-process your own dispatch — never useful, and
+    # on the sync path it deadlocks (see tool_delegate_task). Reject early.
+    if workspace_id and workspace_id == src:
+        return (
+            "Error: cannot delegate_task_async to your own workspace — there is no "
+            "peer who is also you. Do the work yourself, or call commit_memory / "
+            "send_message_to_user directly."
+        )
+
     # Idempotency key: SHA-256 of (source, target, task) so that a
     # restarted agent firing the same delegation gets the same key and
     # the platform returns the existing delegation_id instead of
diff --git a/workspace/tests/test_a2a_tools_delegation.py b/workspace/tests/test_a2a_tools_delegation.py
index 010f4e45..84c2fe0d 100644
--- a/workspace/tests/test_a2a_tools_delegation.py
+++ b/workspace/tests/test_a2a_tools_delegation.py
@@ -127,3 +127,51 @@ class TestPollBudgetEnvOverride:
         # numeric and >= the documented floor (180s healthsweep budget).
         assert isinstance(a2a_tools_delegation._SYNC_POLL_BUDGET_S, float)
         assert a2a_tools_delegation._SYNC_POLL_BUDGET_S >= 180.0
+
+
+# ============== Self-delegation guard ==============
+
+class TestSelfDelegationGuard:
+    """delegate_task / delegate_task_async to your own workspace ID must be
+    rejected immediately (it deadlocks _run_lock on the sync path — the
+    sending turn holds the lock, the receive handler waits for it, the
+    request 30s-times-out). A genuinely different target must NOT be
+    short-circuited by the guard."""
+
+    def _fresh(self, monkeypatch, own_id):
+        import a2a_tools_delegation as d
+        monkeypatch.setattr(d, "WORKSPACE_ID", own_id)
+        monkeypatch.setattr(d, "_peer_to_source", {}, raising=False)
+        return d
+
+    def test_delegate_task_rejects_self(self, monkeypatch):
+        import asyncio
+        d = self._fresh(monkeypatch, "ws-self-abc")
+        out = asyncio.run(d.tool_delegate_task("ws-self-abc", "do a thing"))
+        assert "your own workspace" in out.lower()
+
+    def test_delegate_task_rejects_self_via_explicit_source(self, monkeypatch):
+        import asyncio
+        d = self._fresh(monkeypatch, "ws-other-default")
+        out = asyncio.run(
+            d.tool_delegate_task("ws-X", "do a thing", source_workspace_id="ws-X")
+        )
+        assert "your own workspace" in out.lower()
+
+    def test_delegate_task_async_rejects_self(self, monkeypatch):
+        import asyncio
+        d = self._fresh(monkeypatch, "ws-self-abc")
+        out = asyncio.run(d.tool_delegate_task_async("ws-self-abc", "do a thing"))
+        assert "your own workspace" in out.lower()
+
+    def test_delegate_task_allows_different_target(self, monkeypatch):
+        """Guard passes through for a real peer — it reaches discover_peer
+        (stubbed to 'not found' here) rather than returning the self message."""
+        import asyncio
+        d = self._fresh(monkeypatch, "ws-self-abc")
+        async def _no_peer(*_a, **_kw):
+            return None
+        monkeypatch.setattr(d, "discover_peer", _no_peer)
+        out = asyncio.run(d.tool_delegate_task("ws-OTHER-xyz", "do a thing"))
+        assert "your own workspace" not in out.lower()
+        assert "not found" in out.lower()